What I'm asking is if there was anytime when the water heater was in effect a closed container while it was cooling. If you were to take a 1 gallon tin and heat it in a pan of boiling water then screw on the cover and take it off the heat it would collapse....

What I'm asking is if there was anytime when the water heater was in effect a closed container while it was cooling. If you were to take a 1 gallon tin and heat it in a pan of boiling water then screw on the cover and take it off the heat it would collapse....

Click to expand...

This isn't impossible.
I turned off the supply to the heater, then turned it off. I thought I drained it too.
It may have cooled while warm, with no way to relieve pressure, either negative or positive.
It's not leaking now, other than looking terrible, did I cause permanent damage?

I know exactly what happened to your water heater i have seen that many times before ! !

You have a excessive pressure bulge, caused by not having thermal expansion tank inSTALLED per mfg's spec's
you need the tank between the shut off ball valve and the water heater, when you turned the water heater off it caused excess
pressure to build up and invert the tank ! ! !
YOU HAVE A CHECK VALVE ON THE COLD WATER INLET, YOU MUST HAVE THERMAL EXPANSION TANK BETWEEN ANY VALVES AND THE WATER HEATER

If you look in the fire box you will see the tank setting down on
top of the burner,

this will cause carbon monoxide because the burner cannot burn correctly,
so yes shut heater down now ! !
And get replaced a. S. A. P. Be sure thermal expansion tank is moved to after the shut off valve or you could have the same problem again
e-mail me if you have any more questions

also have plumber correct your vent problem, it may have been that way when you moved in, ! !
But it is you and your family that will suffer because of the incorrect install of this water heater
thats why you should always have a professional do the install and get it inspected by your town people

Judging by what I see in the back ground (DWV) and the heater vent I will guess this was a DIY install...It does appear that there is an expansion tank (failed?) but perhaps that tank is part of the heating system...can't tell from the pic

Whatever the reason the tank was subjected to pressure beyond its working pressure, and maybe even beyond its test pressure. The top "bulged" up, but the flue liner held the center down which is why the pipes bent inward. Discard the tank because it has been damaged beyond repair and its integrity has been compromised. At this time there is no way to tell why it happened.

Thanks hj for the explanation of why the pipes showed the way they do. It makes sense. One question, would this type of flexing cause the glass liner to crack and greatly shorten the service life even if it did not fail from other reasons?